@Luksus so there's an unofficial app that works. Fantastic!
I'm receiving my Nexus 3a in two weeks but
I have a Suunto watch though, which only supports Android and IOS (no web app)

@Dunbrokin this is very good news. Do you mean that the Garmin Connect Android app does work using waydroid? And bluetooth does sync?

Thanks

@Moem thanks a lot. I do have that watch somewhere too. The thing is I do a lot of long trail runs with GPS and altimeter and for relatively good accuracy you need something like a Garmin, Suunto, Coros, Polar or even the latest Amazfit watches.
But all of them are closed source and even on Linux it's a problem to sync them.

Edit:

@Dunbrokin
In the case of Garmin (if I remember fine), you can workaround the FW updates with a computer with a Windows VM and Garmin Express inside.
But Garmin watches are also seen as USB devices on linux and you can manually upload the .fit files using the Garmin Connect web interface.
Then, you can use the web interface to see the data from your phone. It would be really nice to know if the watch could be connected to the phone as an USB device. That would mean that we'd have a workaround for Garmin without waydroid.

So you don't perhaps need the Garmin Android app (using a Linux computer for teh syncs or (perhaps) your ubtouch phone)

The other brands need their respective Android/IOS apps to sync the watch data. As all of them are closed source, the bluetooth stack is somehow needed under waydroid if we need that kind of support.

This is more offtopic but there's also an interesting project here:
https://asteroidos.org/watches
But It is in very early stages supporting only some very basic functions and some few and old smartwatches. No sport functions. But it is an start.

@arubislander totally agree and completely understand.

@arubislander privacy and open source? Please, I'm not here to flame and english is also not my native language.
I'm near 50 and an open source user for , I think, near two decades and I totally understand the problem of going OpenSource in a world It is not. We have running watches, cars with Android Auto, applications that family and friends use or even applications from your company or University... I can only think in a container or a VM that has support for all those things, but that's not easy of course

@Moem I don't know. I'm also new here and I completely understand that this work is made by people and not companies and totally free.

I'm in the same situation with Android.

It's a while I want to move to ubports but my Suunto watch does only sync on IOS and Android and I need bluetooth working fine for that.

Then, there's that WhatsApp thing that everybody uses and I'd prefer not to, but you can't get isolated from the world. It'd be nice to have a native way without waydroid for that but seems impossible ...Lastly some few apps my company uses. So, despite most of us don't want to have Android apps, the thing is a minimal Android support is needed for the real world and most people. Despite we don't like it, that support is needed if we want ubports grow.